B4.2.4—Holozoic nutrition
Holozoic nutrition is heterotrophic feeding by ingestion, internal digestion, absorption and assimilation of organic matter by consumers in ecosystems directly.
- Syllabus
- First assessment 2025
- Objective
- B4.2.4
- Level
- HL
Exam analysis
Chance of appearing1%of analysed past papers
Latest appearanceNovember 2019
Most common paperPaper1
Typical marks1
Common command terms
- Identify
- Outline
Scoring notes
- Common mistake
- Calling an organism heterotrophic without explaining that it feeds on organic matter.
Recent exam appearances
November 2019Paper1 ["HL"] · TZ014[ 1 ]B4.2.4—Holozoic nutrition
Practice this objective
Coverage 2019–2019 · Updated 15 Jul 2026
Holozoic Nutrition Ingests and Digests Food
All animals are heterotrophs, and holozoic nutrition obtains organic matter by ingestion followed by internal digestion, absorption and assimilation.
Food is taken into the body, mechanically and chemically broken into small soluble molecules, moved across the gut wall and incorporated into tissues or used in metabolism.
Sequence: ingestion → internal digestion → absorption → assimilation; indigestible material is egested. Herbivores, carnivores and omnivores differ in food sources but all use this holozoic sequence.
A mammal ingests starch, hydrolyses it to glucose, absorbs glucose into blood and assimilates it by respiration, glycogen synthesis or construction of other molecules.
Ingestion alone is not the complete mode, and egestion is removal of undigested material rather than excretion of metabolic wastes.
Holozoic nutrition
Assessment in practice
1 marksHow it is assessed
This objective is assessed through structured response, multiple choice, commonly using Identify / Outline.
Command terms
Identify / Outline
What earns marks
Build the answer around this relationship: Holozoic organisms ingest organic matter.
Watch for
Calling an organism heterotrophic without explaining that it feeds on organic matter.
Representative question
Question 1
Outline the method of nutrition carried out by P. caudatum.
Niches, Nutrition, And Competition
A niche is the role of a species in a community, including habitat, abiotic tolerances, nutrition, activity, reproduction, and interactions. The evidence should match the question: nutrition mode, oxygen tolerance, feeding adaptation, predator-prey interaction, plant light strategy, fundamental versus realized niche, or competitive exclusion.
- Definition answers should include role plus habitat/resources/interactions, not only place.
- Nutrition modes explain how organisms obtain carbon, energy, or organic matter.
- Adaptation examples should be linked to feeding, defence, light harvesting, or competition.
- Fundamental versus realized niche and competitive exclusion are tested together because interactions narrow where species actually live.
Concept essentials
- Holozoic organisms ingest organic matter.
- Digestion in holozoic nutrition occurs inside the organism.
- Consumers such as herbivores, carnivores and omnivores are holozoic.
- Holozoic nutrition differs from saprotrophic external digestion.